Many portable devices perform current sensing as part of a battery current monitoring function to provide an indication of the battery charge, such as a visual bar indicating the current battery level. During this function, a current sensing circuit typically measures a voltage difference across a known resistance. One common method used for battery current monitoring utilizes a continuous time current measurement. In continuous time current measurement, the current sensing circuit typically uses a single-ended (i.e., a single voltage input to a differential amplifier) measurement that may be susceptible to noise and transients. When sensing smaller currents, as in the case in mobile communication products, the noise and transients may be reflected in the sensed current and thereby significantly affect the accuracy of the sensed current.
Mobile communication products place a premium on maximizing battery life, and measuring the current across a low known resistance minimizes the power drain on the battery during current sensing. For example, in a mobile communication product, the measured voltage difference is typically in the order of about 80 mV Full Scale, and the sensed current reflects the measured voltage difference across the low known resistance as a smaller current.
Additionally, the mobile communication product may use the sensed current to perform other functions that require an instantaneous and relatively accurate current measurement, such as in the order of about a ten (10) bit resolution. For example, the sensed current may be fed to an Analog-to-Digital (A/D) converter to produce a relatively high resolution value of the sensed current for use in a downstream microprocessor. In comparison, conventional continuous time measurements generally provide a measurement on the order of about a seven (7) bit resolution.
Further, the A/D converter, or other downstream component, coupled to the current sensing circuit, may require an input within a pre-determined voltage range that is significantly greater than the measured voltage difference. Although the conventional continuous time measurements generally amplify the measured voltage difference within a single stage, the amplified output is generally limited by the size of the low known resistance. These constraints generally reduce the effectiveness of conventional continuous time measurements for mobile communication products and other devices requiring higher resolution battery current measurements.
Accordingly, a circuit for sensing current is desired having reduced power consumption. In addition, a circuit for sensing relatively low current levels is desired that minimizes circuit component size for battery current monitoring applications, such as in mobile communication products. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.